BREATHING LIFE INTO THE EXTINCTION OF AEPYORNIS WITH EGGSHELL AMINO ACIDS AND STABLE ISOTOPES

The loss of Madagascar’s large land animals was one of the most recent prehistoric mass extinction events to take place on our planet. The extinctions occurred following colonization of the island by people approximately 2000 years ago. Amongst the Malagasy megafauna was a huge flightless bird, Aepyornis. Aepyornis reached weights in excess of 400 kg and laid the largest eggs the world has ever seen, larger than those of any dinosaur. The research aim is to increase our understanding of the timing and causes of the extinction of the genus through the biogeochemical analysis of Aepyornis eggshells.

From heating experiments Arrhenius parameters defining the temperature sensitivity of isoleucine epimerization (measured by A/I) were determined (lnA=40.2, E_a=29.8 kcal/mol). The parameters enable epimerization chronologies from sites with differing thermal regimes to be compared. A set of nine paired eggshell A/I values and radiocarbon ages from southern Madagascar indicates that a good correlation (r²=0.76) exists between these two chronometers. These ages suggest the genus survived until at least the 7th century AD. We have begun to assess the age of eggshell accumulations from several sites (Table Mountain, Nasua, Songoritelo, Ampalora, Beraroha, Belalanda, Faux Cap) along the southwestern coast of Madagascar using A/I values.

Carbon, nitrogen and oxygen isotopes in Aepyornis eggshells are used to trace the flow of nutrients through the prehistoric environments of Madagascar. The isotopes fail to exhibit shifts that would support models explaining Aepyornis extinction in terms of climatic change. The carbon isotopes suggest a diet dominated by C3 plants, or perhaps isotopically light CAM vegetation. Values in excess of 16 per mil for nitrogen isotopes may reflect the effects of water stress on vegetation consumed or on nitrogen cycling within the birds. The minor variation (< 2 per mil) in the oxygen isotopes of Aepyornis eggshell calcite over time suggests that drinking waters were buffered from the isotopic variability produced by evaporative enrichment and meteorological effects. Thus groundwater-fed reservoirs or highland-derived fluvial systems were likely water sources for the genus, at least in the far south.